Mercury levels in surface waters of the Carson River-Lahontan Reservoir system, Nevada: Influence of historic mining activities

Total mercury (HgT), methylmercury (MeHg), and other operationally defined Hg species were determined on water samples collected from a river-reservoir system impacted by historic mine wastes. Simultaneously, a comprehensive study was undertaken to determine the influence of some major physico-chemical parameters on the fate of Hg within the system. Total Hg levels showed an increase from background concentrations of 4 ng liter(-1) upstream of mining activity, to peak values of 1500-2100 ng liter(-1) downstream of Hg contaminated mine tailings piles. MeHg concentrations varied from 0.1 to 7 ng liter(-1) in surface waters. In both cases, peak values were associated with the highest concentrations of total suspended solids (TSS). Particulate Hg (HgP) was typically >50% of HgT and increased downstream. The dissolved fraction of MeHg (MeHgD) always constituted a large portion of total methylmercury (MeHgT). The [MeHgT]/[HgT] ratio decreased downstream suggesting either a high percentage of inorganic Hg input from point sources, or low specific rates of MeHg production within the aquatic system. The latter could be due to the combined effects on microbial populations of both high levels of Hg concentrations found in water and sediments, and other factors related to the aqueous geochemistry of the system. Concentrations of HgT in the water column appeared to be enhanced by inputs of contaminated particles from the watershed during spring snow melt. In the reservoir, significant losses of Hg from the water column were observed. In addition to losses of Hg bound to particles by sedimentation, the removal through volatilization of dissolved gaseous Hg could be an important pathway.     

Freeliving marine nematodes as a pollution indicator of Bohai Sea

A hierarchical diversity index--taxonomic distinctnessindex +, which was first defined by Warwick and Clark in 1998, wasemployed to evaluate the pollution status of the Bohai Sea withfreeliving marine nematodes. The result showed that the Bohai Bayand other coastal sampling sites might be affected by oil and gasproduction and other anthropogenic influences. In other words,anthropogenic disturbance was affecting this component of thebenthos in these locations. And most offshore sampling sites in themiddle of the Bohai Sea were clear and unpolluted.     

Uranium(VL) interactions with OPC/PFA grout

The sorption of uranium on to Ordinary Portland Cement (OPC)/Pulverized Fuel Ash (PFA, fly ash) grout material has been investigated with respect to time, pH, grout:uranium ratio and the chemical composition of the supporting solution. The information obtained is of relevance to the disposal of low-level nuclear waste. The grout material has been chemically characterised and is negatively charged above pH 2.3. At the uranium concentrations studied (2 microM) all uranyl hydroxide aqueous species are expected to be monomeric, rather than polymeric. Uranium(VI) sorption on to the grout material has been explained in terms of inner sphere complexation binding by means of hydroxide bridge formation between the uranium and grout surface. It is also proposed that oligomeric uranyl species are formed across the grout surface, perhaps stabilising the repulsive effects of the negatively charged grout surface and anionic uranyl hydroxide species. Thermodynamic modelling has been used to explain the sorption variation versus solution pH and identifies potential binding mechanisms.     

Investigation of the permeability of humic molecules using zeta potential measurements

Zeta potential measurements have been performed on colloidal humate in the presence of differing concentrations of sodium ions at pH = 6.0. A series of calculations has been performed in which the radius of the humic colloid was varied until the predicted surface potential was equal to the experimentally determined zeta potential. The results of the calculations showed that as the ionic strength increases, the apparent radius of the colloid decreases. Similar calculations in which a model colloid was treated as a rigid sphere, i.e., the radius of the colloid was kept constant, failed to simulate the observed zeta potential measurements.